The Speculist: Sky City


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Sky City

While I was in San Antonio, Texas I spent a lot of time on the River Walk.

The San Antonio River Walk (also known as Paseo del Rio) is a network of walkways along the banks of the San Antonio River, one story beneath downtown San Antonio, Texas. Lined by bars, shops and restaurants, the River Walk is an important part of the city's urban fabric and a tourist attraction in its own right.

Today, the River Walk is an enormously successful special-case pedestrian street, one level down from the automobile street.



Back in the 1920's there was talk about paving over the San Antonio River. The buildings that surrounded it had basement levels on the water, but nothing too important could be stored at that level because the river was constantly flooding. But once the river was tamed - and demonstrated to be safe after heavy rainfall - development could begin. That flooded basement space often became the most valuable part of those old buildings as they were turned into shops and restaurants. The River Walk is now more of a tourist attraction than the adjacent Alamo.

This was a special case. Most cities don't have a little river that can be developed like this. But it seems to me that the idea of taking space that isn't fully utilized and making a pedestrian street at a separate level from the main street could work elsewhere.

Modern urban living has been made possible by three technologies:

  • Steel construction,
  • the elevator, and
  • air conditioning

These three together have made it possible to build vertically. Take away any one of these three and cities wouldn't look anything like what we have today. Building vertically has a multiplier effect on the usefulness of land in a city. Imagine how much land Manhattan would have to cover if it were limited to one-story structures.

The Conde Nast Building contains 1.6 million square feet of floor space, and it sits on one acre of land. If you divided it into 48 one-story suburban office buildings, each averaging 33,000 square feet, and spread those one-story buildings around the countryside, and then added parking and some green space around each one, you'd end up consuming at least 150 acres of land. And then you'd have to provide infrastructure, the highways and everything else." Like many other buildings in Manhattan, 4 Times Square doesn't even have a parking lot, because the vast majority of the six thousand people who work inside it don't need one.

Looking at a skyscraper like this shows us how important a transportation device the elevator is. An elevator in a vertically built city can take the place of hundreds of cars elsewhere.

But building vertically progressively isolates space the further up the structure you move. We learned on 9/11 that this isolation can be dangerous. But take a mundane problem: Let's say you're on the 20th floor of a building and you see your buddy in the building next door. Getting over there will require time and a couple of elevator rides. You are within feet of each other but might as well be a mile apart.

There's a relatively simple idea that's been around for decades that could be just as transformative as the three I mentioned, but has not yet been fully exploited - the skyway or sky bridge. Most cities of any size already have several. Three in my home town are connected to hospitals. They pull together the main hospital and separate clinics and parking garages.

But skyways could be used on a much larger scale.

The largest continuous network of skyways - the Minneapolis Skyway System - spans 8 miles connecting 69 blocks in downtown Minneapolis. Other cities in the Midwest, such as Des Moines, Cedar Rapids, Rochester, and Saint Paul also have significant skyway systems.
Minneapolis skyway.jpg

This skyway system was Minneapolis' answer to the cold weather problem. Toronto and Montreal went a slightly different route - they built underground cities to get away from the cold.

A skyway network doesn't have to be reserved to cities that experience extreme weather. Think of any city building. The busiest floor of the building is at the street level. For most buildings it's the only level that connects the building with the rest of the world. A network of skyways would add connections at other levels.

These new skyway streets could be for foot traffic only, or perhaps bikes, segways, or moving sidewalks. They could be opened or enclosed; elaborately styled or Spartan. However designed this network would bring street level foot traffic into the sky and would expand on the existing multiplier effect of modern vertical construction.

Without expanding the footprint of a city one inch, you could build a second city in the sky.


Without expanding the footprint of a city one inch, you could build a second city in the sky.

Cool idea -- very Jetsonesque. I understand that in Minneapolis, the skyway access tunnels are referred to colloquially as hamster tubes.

Another take on the separation of vehicle and pedestrian traffic is the old mining town of Guanajuato, Mexico. The town was built pre-auto, in the mountains. For the last 100 years, the town has used its mining expertise to construct tunnels underneath the town for vehicle access. The tunnel system is being continuously expanded, preserving the density and quality of life in the town center, while allowing access to town for people and goods. For tunnel pictures, Google images has plenty of examples.

Needless to say, your GPS navigation system is pretty much useless for driving around town.

I love this. I think it is a great solution to sprawl and traffic. I wonder how difficult it would be to retrofit existing buildings with systems like this, that seems to be the biggest roadblock.

Dallas as a tunnel/skyway/underground mall system downtown.

Let's say you're on the 20th floor of a building and you see your buddy in the building next door. Getting over there will require time and a couple of elevator rides. You are within feet of each other but might as well be a mile apart.

Existing sky malls don't solve this problem - they're at best only a level above the street. Connecting buildings 20 floors up would be an interesting challenge ...

As laugh-In would have it "very interesting".
Whilst a commendable expansion of existing transport systems, there are always attendant issues.
Need to define ownership & responsibiltiy for risks arising from skybridges eg.
suicide proofing, fire-seperation of buildings, control of disruptive "rubberneckers/ tourists", collision risks re emergeny flying vehicles such as police and air ambulances. The best issue is what happens when one building has to be demolished, also in many jurisdictions many titles don't issue or hold "air rights " above a maximum stated heightabove ground level , or have prohiobitons or setbacks to allow solar access to other adjoiniung sites etc. Many proposed urban wind generation designs would need skybridges for access & servicing, so as an isue it will develop.So , on balance, not as clear cut as a building built "titled" piece of land. The risks about directing occupant volumes in the case of fires for example, 9/11 might just have concentrated greater numbers of people in riskier situations: much harder to model "connected systems" re occupant behaviour in smoke & fire hazard settings. Still thought provoking!. I like the description "Hampster tubes", sort of fits the "organizational zoo" parlance.

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